1. Field of the Invention
The present invention relates to a battery device including a charge/discharge control device configured to control the charging and discharging of a secondary battery.
2. Description of the Related Art
A battery device of the related art is illustrated in a circuit diagram of FIG. 3.
The battery device of the related art includes a secondary battery 11, a charge/discharge control device 23, an external positive terminal 24, and an external negative terminal 25. The charge/discharge control device 23 includes an Nch discharge control field effect transistor 16, an Nch charge control field effect transistor 17, a charge/discharge control circuit 14, resistors 12 and 15, and a capacitance 13. The charge/discharge control circuit 14 includes a positive power supply terminal 18, a negative power supply terminal 19, a discharge control signal output terminal 20, a charge control signal output terminal 21, and an overcurrent detection terminal 22.
The charge/discharge control circuit 14 monitors the voltage of the secondary battery 11 by keeping track of a voltage that is applied between the positive power supply terminal 18 and the negative power supply terminal 19. When the voltage of the secondary battery 11 exceeds an overcharge detection voltage, the charge/discharge control circuit 14 outputs a charge prohibiting signal from the charge control signal output terminal 21 to turn the Nch charge control field effect transistor 17 off, to thereby stop charging. This is called an overcharge detection function. When the battery voltage of the secondary battery 11 drops below an overdischarge detection voltage, the charge/discharge control circuit 14 outputs a discharge stopping signal from the discharge control signal output terminal 20 to turn the Nch discharge control field effect transistor 16 off, to thereby stop discharging. This is called an overdischarge detection function.
The charge/discharge control circuit 14 also monitors a current flowing in the battery device by keeping track of the voltage of the overcurrent detection terminal 22. When the voltage of the overcurrent detection terminal 22 exceeds a discharge overcurrent detection voltage, the charge/discharge control circuit 14 outputs a discharge stopping signal from the discharge control signal output terminal 20 to turn the Nch discharge control field effect transistor 16 off, to thereby stop discharging. This is called a discharge overcurrent detection function. When the voltage of the overcurrent detection terminal 22 drops below a charge overcurrent detection voltage, the charge/discharge control circuit 14 outputs a charge prohibiting signal from the charge control signal output terminal 21 to turn the Nch charge control field effect transistor 17 off, to thereby stop charging. This is called a charge overcurrent detection function.
Currently, battery devices that include two charge/discharge control devices are often used as more safe battery devices. Providing a battery device with two charge/discharge control devices means that, in the event of a failure of a first charge/discharge control circuit to operate, a second charge/discharge control device comes into operation, and hence safety of the battery device is enhanced.
However, battery devices of the related art that include two charge/discharge control devices have a problem in that, when the second charge/discharge control device detects discharge overcurrent and then the first charge/discharge control device detects overcharge, removing a load that is the cause of the discharge overcurrent does not always result in a successful return to a normal state because the detection of overcharge turns off the Nch charge control field effect transistor and the removal of the load accordingly does not change the voltage of the overcurrent detection terminal in the second charge/discharge control device.